Two strong links
Connect two candidate pairs for the same digit. At least one of the two outer cells must contain that digit.
In row 2, the only places for 3 are R2C3 (A) and R2C4 (B). In column 5, they are R6C5 (C) and R1C5 (D). Since B and D share box 2, they cannot both be 3. This forces 3 into at least one of A and C. Remove candidate 3 from every other cell that shares a row, column or box with both A and C.
What to look for
A strong link connects the only two candidate positions for a digit in a house. One of the two cells must contain it. Find two such links where a cell in one pair shares a row, column or box with a cell in the other pair. This pattern includes the Skyscraper and the 2-String Kite. The hints never chain more than two links together.
Why it works
Call the pairs A-B and C-D, with B and D sharing a house. If A does not contain the digit, B must contain it. That rules it out of D, so C must contain it. At least one of A and C must therefore contain the digit.
Try it step by step
- Find two strong links for the same digit.
- Check that the inner cells B and D share a row, column or box, so they cannot both contain the digit.
- Remove the candidate from every other cell that sees both outer cells A and C.
Try it on a real puzzle
Start with the highlighted step, then keep solving. Use "Apply hint" to make the suggested change, or enter your own digits and candidate notes. Use "Undo" to reverse your last change.
| C1 | C2 | C3 | C4 | C5 | C6 | C7 | C8 | C9 | |
|---|---|---|---|---|---|---|---|---|---|
| R1 | |||||||||
| R2 | |||||||||
| R3 | |||||||||
| R4 | |||||||||
| R5 | |||||||||
| R6 | |||||||||
| R7 | |||||||||
| R8 | |||||||||
| R9 |
Use the arrow keys to move, 1-9 to enter a digit and Backspace or Delete to clear a cell. To add or remove a candidate, press C and then 1-9.
Source puzzle number: 168873 · Play this puzzle from the start
A simple example
The board labels the two links A-B and C-D. A cell that shares a row, column or box with both A and C cannot contain the linked digit.
A house is a row, column or 3 × 3 box. A line is a row or column. Two cells "see" each other when they share a house. R1C3 means row 1, column 3. Boxes are numbered 1-9 from left to right and top to bottom. Braces such as {1, 2} show a cell's candidates, not confirmed digits.